The present invention relates to structure for keeping clean the interior surfaces in the headbox of a paper machine as well as for contributing to the homogeneity of the stock which flows through the headbox.
It is known that there is a tendency for matter such as fibers, fillers, or slime to adhere to and accumulate or build-up at interior surfaces of a headbox of a paper-manufacturing machine. These slime deposits may be of biological or non-biological origin.
The tendency of such contamination to occur in the interior of a headbox of a paper-manufacturing machine depends to a great extent on the design of the headbox, which is to say on the way in which flow velocities of the stock are arranged in different parts of the headbox. It can generally be assumed that locations which are particularly susceptible to contamination by build-up of matter as referred to above are those where the flow of stock is relatively slow as compared to the velocity of flow at other locations in the interior of the headbox. At such locations where there is a relatively low flow velocity for the stock dirt of other matter will begin to accumulate, even during perfectly normal types of operation, if the particular type of stock and other conditions are favorable for such contamination to take place.
In order to attempt to solve this problem it is known to utilize in a headbox flow channels shaped in order to achieve as much as possible a flow of stock which approaches as closely as possible to the ideal, and for this purpose such flow channels have ground or polished surfaces in order to achieve as great a smoothness as possible. Moreover, in paper mills it is known to utilize suitable additives in the pulp stock such as, so-called anti-slime agents.
However, even though attempts of the above type have been made to reduce the tendency of contaminating deposits to buildup at certain locations in the interior of the headbox, the desired results have not always been achieved. In fact it is necessary from time to time to completely shut down the paper machine only for the purpose of cleaning the headbox.